A method for controlling an internal combustion engine is discussed in the publication DE 10 2013 223 489. In the method discussed there, an injection process is subdivided into at least three partial injections. Different parameters are selected to ensure that the noise emissions are as low as possible. The interval between the individual partial injections and the subdivision of the injection quantities to the individual partial injections are predefined accordingly, in the form of parameters. This injection pattern is also referred to as “pine tree pattern”.
Modern internal combustion engines use different injection patterns depending on the load and the rotational speed of the internal combustion engine. In the partial load range, for instance, the so-called “pine tree injection pattern” is used. This offers advantages as far as the reduction of combustion noise is concerned. The combustion noise is simply referred to as noise in the following text. At higher loads, the injection pattern changes toward boat or block injections. The combustion noise is of lesser concern here since the driving noise predominates. The block injection is characterized in that the fuel is supplied to the combustion chambers essentially in a single injection procedure. One or more preinjection(s) and post-injection(s) may possibly be provided. The main injection, on the other hand, takes place in the form of one injection. In the boat injection, a smaller injection rate is selected at the start of the injection. That means that a smaller fuel quantity per time unit or angle unit is injected. In the pine tree injection, the main injection is subdivided into numerous partial injections, usually three or more; these are difficult to distinguish from the post-injection and/or preinjection.
Each subdivision of the injection quantity into further injection types means further charge and discharge processes of piezo actuators and thus increased power losses of the control unit. As a rule, certain injection patterns, such as the pine tree pattern, are therefore not to be used in all operating states. The pine tree pattern may be employed only in cases where it is useful, which is the case at low loads and/or small rotational speeds, in particular.
In other words, a switchover as a function of the operating state must take place between injection patterns. These switchovers result in partially abrupt changes in the noise emissions. Such changes in the switchover of the injection patterns at slight changes in the operating point of the internal combustion engine may be perceived as annoying by the driver and possibly be interpreted as an error.